1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting a specimen on which a pattern is formed, e.g., a wafer in manufacture of a semiconductor device and, more particularly, to an optics in an optical inspection apparatus.
2. Background Art
Manufacture of a semiconductor device is divided into a front end process and a back end process. The front end process includes isolation forming, well forming, gate forming, source/drain forming, interlayer dielectric film forming and planarization. In the back end process, contact plug forming, interlayer dielectric film forming, planarization and metal wiring forming are repeated and passivation film forming is finally performed. In the course of the above-described manufacturing process, wafers are extracted and inspection of defects is performed. The defects include foreign particles on the wafer surface, scratches in the wafer surface, and pattern defects (such as shorts, opens and via missing). The first objective of defect inspection is to control the condition of the manufacturing apparatus, and the second objective of defect inspection is to ascertain a process step in which a defect is caused and the cause of the defect. With the miniaturization of semiconductor devices, a demand has arisen for increasing the sensitivity of inspection apparatuses.
For example, several hundreds of semiconductor devices (called chips) having patterns identical to each other are made on one wafer. With an inspection apparatus, therefore, a method of comparing images between chips adjacent or close to each other is mainly used.
An inspection apparatus in which a wafer is irradiated with light and dark-field images are compared is being widely used for inline inspection because of its high throughput. A first related known art is use of a refractive optics constituted of lenses with respect to a dark-field inspection apparatus in an ultraviolet region. For example, JP Patent Publication (Kohyo) No. 2005-517906 (patent document 1) relates to this art. The patent document 1 describes that the field of view of the optics is in the form of a straight slit having a longer-side size of several millimeters, and that high-throughput inspection can be performed by scanning a wafer along the shorter-side direction.
A second related known art is use of a reflective optics constituted of mirrors with respect to an inspection apparatus of a wide wavelength band from a visible light region to a vacuum ultraviolet region. In the second related art, the reflective optics can be used in a wide wavelength band because it has no chromatic aberration. Inspection with high sensitivity is made possible by selecting a wavelength band according to the manufacturing process and a defect of interest. For example, JP Patent Publication (Kohyo) No. 2008-534963 (patent document 2) relates to this art.    Patent document 1: JP Patent Publication (Kohyo) No. 2005-517906    Patent document 2: JP Patent Publication (Kohyo) No. 2008-534963